Carburetor



' C. H. KIRBY CARBURE'I'OR Original Filed April 23, 1932 April 7, 1936.

7 Sheets-Sheet 2 agw 7/74 a a, m E1 a a w M April 7, 1936. c. H. KIRBY R19,916

' CARBURETOR Original Filed April 2J5, 1932 7 Sheets-Sheet 3 April 7,1936. 4 c. H. KIRBY F 19,916

- CARBURETOR Original Filed April 23, 1932 7 She ets-Sheet 4 April 7,1936. c. H. KIRBY 19,916

I CARBURVETORY Original Filed April 23. 1932 Sheets-Sheet 6 ate/29 75 1(1. H. KIRBY 'CARBURETOR Ori gi nal Filed April 25, 1952 April 7, 1936.

7 Sheets-Sheet 7 w x w 1 A Z r1 KUWLW.

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Reissued Apr. 7, 1936 PATENT OFFICE CARBURET'OR Charles H. Kirby, Flint,Mich., assignor to Marvel Carburetor Company, Flint, Mich., acorporation of Illinois Original No. 1,931,259,

dated October 17, 1933,

Serial No. 607,053, April 23, 1932. Application for reissue September21, 1935, Serial No.

11 Claims.

This invention relates to carburetors for internal combustion enginesand has special reference to a carburetor having improved meteringcharacteristics in the upper part of the power range.

It is well known in the art that it is difficult to combine satisfactoryidling and maximum power characteristics in a plain tube carburetor witha single venturi since if the venturi is large enough for maximum powerit will be diflicult to provide sufficient suction at the fuel nozzleoutlet to lift the required amount of fuel to maintain a proper mixtureratio at extreme low engine speeds, and, with the same setting, avoidundue mixture richness at some points above the extreme low enginespeeds. Several solutions of this problem have been attempted, such asconcentric venturis and various attempts at metering the fuel over theeconomy range, and 20 it is accordingly an important object of thisinvention to provide an improved carburetor wherein the meteringcharacteristics have been adiusted to more perfectly suit the enginerequirements over a wide operating range. I accomplish this improvedresult by providing a relatively unrestricted venturi in a plain tubecarburetor and provide substantially separate fuel metering suppliesthereto one of which is the usual form of suction actuated delivery 30metered by submerged calibrated orifices or jets. Since this form offuel delivery has the faults previously mentioned I provide asubstantially separate secondary fuel supply embodying an overflowing orpressure head at the nozzle delivery point this secondary fuel supplybeing mechanically controlled in accordance with the engine operatingconditions as by the engine suction as distinguished from the suctionwithin the carburetor adjacent the fuel discharge noz- 40 zle. Thus onefuel supply supplements the other since the overflowing nozzle can bearranged for either constant delivery or variable delivery in responseto suction thereon, according to the arrangement of the air bleed there-45 into. One form of my invention has been shown in connection with ananterior throttle type of carburetor wherein the carburetor nozzles aresubjected to manifold suction which as is well known varies from amaximum at idling to a minimum at wide open throttle and slow operatingspeeds. With this arrangement it is necessary to modify the suction onthe primary nozzle system since maximum suction coincides with minimumfuel requirements, when the secondary fuel system has been shut off. Y

Plain tube carburetors with suction actuated fuel feeds, even ifprovided with a compensating fuel system, depend for fuel delivery uponsuction within the carburetor and lag in delivery due to the height thefuel must be lifted as well as the surface tension of the liquid fuel. Apositive head on the fuel delivery is ideal for normal operatingconditions but supplies an overrich mixture under conditions of lowdemand, and a lean mixture at the other end of the scale where aslightly overrich mixture will produce the maximum power of the engine.I overcome these drawbacks by providing a primary fuel system responsiveto suction thereon and supplement this with a gravity flow fuel systemwhich compensates for the leanness of the suction responsive nozzle atpart load and is itself restricted at higher loads by an air bleedadjusted to engine requirements, since under such conditions the suctioncontrolled nozzle is capable of supplying a greater proportion of thefuel needed to maintain proper mixture proportions for maximumperformance. It is accordingly an object of this invention to providean. improved carburetion system which combines two divergent fuel supplysystems in such a Way as to balance each by the other to obtain agreatly increased range of performance maintained at the maximum economyconsistent with operating requirements.

It is a further object of this invention to provide an improved plaintube carburetor capable of developing the maximum power output of agiven' engine while maintaining desirable part load operatingconditions. I accomplish this result by providing a plain tubecarburetor, having a suction controlled primary nozzle system, with asecondary nozzle system supplied with fuel under a positive or statichead above the nozzle outlet, fuel being supplied in excess quantitiesto a well feeding the secondary nozzle system and overflowing from thewell into a lower fuel bowl containing the usual float operated fuelinlet valve controlling the fuel supply to the well.

It is a further object of this invention to provide an improved fuelsupply system involving a static or pressure head wherein the fuel flowis under the control of a valve adapted to shut oil in response toidling conditions such as high manifold suction or a closed throttle.

It is also an object of this invention. to provide an improved andsimplified carburetor of superior automatic metering characteristics notsubject to derangement or maladjustment in service.

Other and further important objects of this invention will be apparentfrom the disclosures in the specification and the accompanying drawings.

This invention (in a preferred form) is illustrated in the drawings andhereinafter more fully described.

On the drawings:

Figure 1 is a vertical section through an updraft carburetor embodyingthe features of this invention.

Figure 2 is a reduced plan view of the carburetor shown in Figure 1.

Figure 3 is a fragmentary section on the line III-III of Figure 2.

Figure 4 is a fragmentary section on the line IVIV of Figure 2.

Figure 5 is a fragmentary section of a carburetor similar to that ofFigure 1 embodying a modified form of nozzle structure.

Figure 6 is a fragmentary section similar to Figure 4 embodying amodification in the air bleed arrangement.

Figure '7 is a plan view of a downdraft carburetor embody ng thefeatures of this invention.

Figure 8 is a section on the line VIII-VIII of Figure '7.

Figure 9 is a section on the line IXIX of Figure '7.

Figure 10 is a section on the line X-X of Figure '7.

Figure 11 is a section on the line XI-XI of Figure '7.

Figure 12 is a section on the line XII-XII of Figure 11.

Figure 13 is a diagrammatic assembly of the features of the carburetorshown in Figures 7 to 12.

Figure 14 is a plan view of a carburetor similar to that of Figures '7to 13, wherein a throttle control has been substituted for the suctioncontrol of the fuel flow from the gravity nozzle.

Figure 15 is a section on the line XV--XV of Figure 14.

Figure 16 is a fragmentary section of the throttle control of Figure 14as applied to the carburetor of Figures 1 to 6.

As shown on the drawings:

The updraft type of carburetor illustrated in Figures 1 to 6 comprises abody member 20 containing a fuel chamber 2|, and a mixing chamber 22with an elbow air inlet 23 thereto controlled by a choke valve 24 on ashaft 25. The fuel chamber 2| feeds into a passage 26 through acalibrated metering jet 21, the passage 26 having a tube 28 forming adischarge nozzle subject to the suction at the throat of a venturi 29mounted in a mixture outlet passage 30 in a cover member 3|, the outletpassage terminating in the usual mounting flange 32, and containing thebutterfly throttle valve 33 on a shaft 34 operated by a lever 35.

An idling mixture passage 36 contains a calibrated metering jet 31 andleads from the passage 26 up to an idling adjustment needle valve 38controlling the admixture of air from the mixing chamber 22 through aport 33. The idling passage 36 terminates in a chamber 40 adjacent theedge of the throttle valve when the latter is closed, passages 4| and 42leading from the chamber 40 to above and below the edge of the throttlevalve as shown in Figure 1. With this construction the high suctionabove the throttle under idling conditions serves to draw fuel throughthe jet 3! and. air through the port 39 as well as air from below theedge of the throttle through the passage 42, control of the idlingmixture proportions, after the jet 3'! has been selected, residing inthe idling adjusting needle valve 38 which controls the admission of airbelow the chamber 46.

The carburetor is provided with a throttle operated accelerating pump tobe described in connection with that embodiment of .the inventiondisclosed in Figures 7 to 12, the pump delivering through passages 43and 44 shown in Figure 1 as opening into the chamber 26 below a plug 45therein which contains a calibrated metering jet 46.

The foregoing described structure is a. more or less simple form ofcarburetor which differs from the conventional plain tube carburetor ofthis type in that the venturi is .relativelylarge and unrestricted sothat maximum power may be obtained. The venturi is in fact so large asto be inadequate to create sufficient suction on the fuel nozzle atnormal part load operating conditions so that the carburetor as so fardescribed would be entirely unsuitable for other than idling and fullload operation at high engine speeds; the intermediate range and thefiner mixture control therefore being cared for by a secondary fuelnozzle system to be presently described.

The secondary or pressure fuel supply is best shown in Figure 3 whereinit is combined with the fuel admission to the carburetor. Fuel issupplied in any convenient manner to an inlet passage 41 formed in aboss 48 on the cover and is admitted past a float controlled valve 49 toa chamber 50 in the cover. The float 5| and float valve 49 are soarranged that there is no direct flow from the chamber 50 to the floatchamber 2|, the fuel flowing into a well 52 and overflowing therefromthrough a passage 53 leading to the float chamber. full of fuel to alevel above that of the float chamber and also considerably above theoutlet of the primary nozzle tube 28. The well 52 contains a valve guidemember 54 having a, valve seat 55 discharging into a passage 56 leadingto an annular chamber 51 surrounding the primary nozzle tube 28, anenveloping tube 53 forming the secondary nozzle and terminatingconsiderably below the level of the fuel inthe well 52 so that anappreciable pressure or static head of fuel causes discharge through thenozzle as long as the passages thereto are open.

This pressure or static head is supplemented by suction on the nozzleoutlet at high rates of air flow through the venturi such as occur inthe power range and in order to control the suction effect on the nozzletube 58 it is desirable to air bleed the same. Figures 4 and 6 showtwoair bleeding arrangements which may be selected to control the fueldelivery in accordance with the requirements of a given engine design.In Figure 4 by providing a calibrated orifice 59 admitting air from themixing chamber 22 to the passage 56 the variable suction in the mixingchamber as well as the restricted orifice 59 will serve tovary the fuelfeed per unit of time in accordance with variations in operatingconditions. On the other hand an unrestricted atmospheric vent 60 to thepassage 56, located above the level of thefuel in the well 52, as shownin Figure 6, will serve to give a constant rate of fuel flow regardlessof suction conditions within the car- Thus the well is maintainedburetor. The air bleed of Figure 4 can be so chosen as to vary the fuelflow in step with engine requirements over and above the supply due tosuction on the primary or suction nozzle 28, so that varying enginerequirements can be predetermined and allowed for without the furtherneed of field adjustments subject to the manifold idiosyncrasies ofindividual operations or service men.

Since the nozzle tube 58 is below the level of the fuel in the well 52the fuel naturally tends to overflow to the bottom of the mixing chamber22 upon stoppage of the engine. A drain hole 6| may be provided, but ifthere is any ob jection to such overflow the inner or primary nozzletube 28 may be made shorter than the outer tube as shown in Figure 5, inwhich case the fuel in the outer nozzle 58 flows back through the innernozzle 28 to the chamber 26 and thence to the float bowl 2| through thejet 21, raising the float 5| until the float valve 48 cuts off furtheradmission of fuel.

The fuel flow past the valve seat is under the control of a valve 62normally held away from the seat by a spring 83. This valve is providedprimarily as a shut off valve when the engine is operating under idlingconditions and the preferred method of control thereof is shown inFigure 3 where a vacuum chamber 64 contains a piston 85 reciprocabletherein which is provided with a stem 86 engaging the head of the valve62. A suction passage 61 connects the lower part of the chamber 64 withthe carburetor outlet passage 38 above the throttle therein, so that thepiston is drawn downwardly by high suction on the engine side of thethrottle valve. Since the maximum suction at this point occurs with aclosed throttle under idling conditions it will be seen that with aproperly chosen spring 83 the valve 82 will be closed under idlingconditions when the idling bypass is operative, and that as the throttleis opened the suction acting on the piston will decrease in value untilthe spring 83 lifts the valve 62. The upper part of the chamber 64 canconveniently be vented through a cap 68 to prevent retardation of thepiston movement. The strength of the spring 63 can be predetermined inrelationship to the chamber size and manifold vacuum to cause the valve62 to initially open at any desired point in the operating range abovenormal idling.

The foregoing suction control of the secondary fuel supply is directlyresponsive to variations in pressure which cause fluctuations in thedelivery from the primary fuel nozzle system and is therefore thepreferred form of the invention. However since engine suction is largelydetermined by the position of the throttle under idling conditions, thecontrol of the valve 62 may be derived directly from the throttle asshown in Figure 16 where a cam 69 has been applied to the throttle shaft34 and operates through a bell crank 10 to lift the valve 82 when thethrottle is opened, by means of a plunger ll, the valve 62 beingnormally held closed by a spring I2. It will be evident that in thismodification the cam can be varied in profile to obtain any desiredpoint and degree of opening relative to throttle movements to secure asupplemental or secondary fuel supply that will compensate for thedeficiencies in the rate of fuel supply from the primary or suctionoperated nozzle 28.

The downdraft type of carburetor illustrated in Figures '7 to 15 hasmany of the features described in connection with the updraft typepreviously described, so that for the sake of simplicity the samereference numerals will be used in describing theparts of the downdraftcarburetor that are similar in structure and function to those of thefirst described carburetor.

The downdraft carburetor comprises a body member 13 providing an airinlet passage 14 in which the throttle 33 is mounted, the passage 14leading to a downwardly discharging outlet passage 15, containing theventuri 28, and terminating in the usual mounting flange 32. Thus thearrangement shown provides an anterior throttle which also replaces theusual choke valve and renders the fuel nozzle outlets subject tomanifold or engine suction at all times. Since manifold suction is amaximum under idling conditions it is necessary to limit or shut off theflow of fuel to the primary or suction nozzle tube 28 as well as fromthe secondary gravity or pressure nozzle 58, the outer end. of which isbent downwardly in the direction of the air flow. The end of the suctionnozzle tube 28 is cut off inside the outer tube to avoid the syphoneffect that might result were it carried down to the outlet of the outertube.

Fuel is supplied to the primary nozzle system from a float bowl itapplied beneath the body member '53, the various parts of the primarysystem being arranged in a boss H depending into the bowl from the bodymember. Compensation for the increased suction under idling conditionsis provided by a metering pin 78 carrying head 18 yieldingly held by aplunger 88 which is adapted to be pressed downwardly by a cam 8! carriedby the throttle shaft 34 the cam contacting an adjustable tappet 82 forcontrolling the location of the metering pin 18 relative to a taperedorifice 83 which admits fuel from the bowl to a chamber 84 in which theplunger operatesv The plunger is normally urged upwardly by a spring 85and is limited in its movement by a set screw 86 engaging in anelongated slot 8! in the plunger. Fuel entering through the orifice 83is delivered through the passage 88 to the nozzle tube 28. The chamber84 is also provided with an air bleed passage 89 having a restrictedinlet 88 within the bowl above the liquid level therein.

When the throttle valve is fully closed the metering pin 18 closes theorifice 83 and it is therefore desirable to provide a priming mechanismcomprising a secondary fuel inlet passage 81 bypassing the orifice 83and normally closed by a valve 82 held down by a spring 93. By liftingup on the head 94 of the valve 82, by means of any suitable primeroperating mechanism, the valve 92 is lifted off its seat and allows thechamber 84 to fill, although fuel is not delivered. from the nozzle 28until engine suction acts thereon.

The accelerating pump structure shown in Figure 10 is common to bothforms of carburetors; comprising a pump cylinder 95 containing areciprocable piston 96 operatively connected to the throttle cam by alink 91 to be operated. by an opening movement of the throttle. Thepiston is ported at 98 and has a free follower 99 thereabove whichserves to: give a prolonged accelerating charge since a rapid downwardmovement of the piston will force fuel through the port 98 thusretarding the downward move ment of the follower until the piston stopsmov-- ing whereupon the follower acts as a second piston to return theescaped fuel tothe pumping cylinder below the piston. Fuel is admittedto the cylinder through the plug I88 which'contains a check valve l8l,fuel being delivered through a passage I02 and nozzle I03 (both showndotted in Figure 10) to the air inlet passage I4. The nozzle I03actually does not reach the passage but sprays through an orifice I04therein which also serves as a vent for the float bowl since it isanterior to the throttle.

The secondary fuel system is substantially similar to that described inconnection with the first type of carburetor, since as shownin Figures11 and 12 the float 5I controls the admission of fuel past the valve 48at the inlet 41 and this fuel flows along the passage 50 to the Well 52,excess fuel overflowing from the well to the float chamber through thepassage 53. The well feeds fuel past the valve 62 into the passage 56leading to the outer nozzle tube 58. The previously described types ofair bleeds to the passage 5-6 may be used although'only the externalbleed 60 has been shown in Figure 12, a restricted orifice I05 beingshown in connection therewith. The same variations of valve control,comprising a suction control of the valve 62, as in Figures 11 and 12;and a throttle control as in Figures 14 and 15, are provided, thethrottle cam 69 in the latter embodiment serving to directly lift thevalve 62 through an offset pin I06 carried by the member II.

The operation of the carburetor of this invention may conveniently beconsidered in two stages, since the characteristics of the primary fuelsystem in some respects are opposed to those of the secondary or gravityfuel system and the two thus complement each other,

The primary or suction controlled fuel system of the updraft carburetoris best shown in Figure 1 wherein the calibrated metering jet 2'I limitsthe fuel delivery to the nozzle tube 28 at high suctio-ns thereon,corresponding to maximum demands with wide open throttle. Since the fuellift required at the nozzle tube outlet precludes delivery underconditions of a slight pressure drop in the mixing chamber 22 it isusual to provide an idling bypass 36 which is subjected to the highmanifold suction created by a nearly closed throttle. When the primaryfuel supply comes into action the delivery therefrom increases rapidlyas a function of the suction in the mixing chamber, until the capacityof the metering jet 21 is reached. Thereafter the increase is less rapiduntil it reaches a maximum under full power conditions. The primary fuelsystem is of course proportioned so that at the maximum the enginerequirements are not ful- 1y satisfied since the fuel supplied is not aconstant proportion of the engine requirements.

The secondary or gravity head fuel supply to the outer nozzle tube 58would obviously overfiow as long as fuel is supplied to the carburetorso that the shut-01f valve 62 actuated by either the manifold suction orthe closing of the throttle serves to prevent the secondary fuel systemfrom coming into action untilthe idling bypass supply tapers off due tothe initial opening movement of the throttle. Opening of the throttlealso decreases the manifold suction differential allowing the suctioncontrolled valve to open thus causing the secondary fuel system to coverthe gap left by the falling off of the idling supply. The secondary fuelsystem delivers a substantially constant fuel flow until suction acts onthe nozzle to accelerate this flow. Thereafter, with an increasingdemand, this increasing suction brings the primary system into initialand increasing action sufficient to maintain proper and economicalmixture proportioning over the intermediate power range of the engine.

The secondary fuel supply can be air bled as previously described toeither maintain a constant flow regardless of suction acting on thenozzle, or to respond in varying degrees to suction increases, asrequired to compensate for the varying proportion of the fuel supplyfurnished by the primary or suction responsive fuel system. Thus thecombination of the two fuel systems can economically covelr the fullrange of operating conditions without localized intervals ofover-richness or leanness in the mixture proportioning.

The anterior throttle type of downdraft carburetor illustrated inFigures 7 to 15 chiefly differs from that previously described, in the,control of the primary or suction responsive fuel feed. This is becausethe anterior location of the throttle imposes manifold suction on thenozzle outlet and. the pressure differential causing fuel flow istherefore a maximum under idling conditions and tapers off as thethrottle is opened. The metering arrangement of Figures 9 and 10 istherefore provided to cut off the flow of fuel to the primary nozzlewhen the throttle is closed by means of the cam 8| which pushes themetering pin I8 downwardly in the tapered orifice 03 to stop the flow offuel. The cam is so formed as to result in prompt partial retraction ofthe metering pin when the throttle is opened sufiiciently for idlingthus providing a gradually increasing fuel supply covering idling andthe transition interval to part load operation. The chamber 84 is airbled through the passage near the bottom thereof to prevent suction fromaffecting the metering of fuel through the orifice 03. With thisarrangement, the fuel flow through the primary system, after themetering pin reaches its upper position, does not increase as rapidly asin the first described form where the suction on the nozzle increasedout of proportion to the increased air flow. The secondary or pressurefuel system operates in the same way as before except that it isdesirable to have the delivery respond somewhat to the injector effecton the nozzle at large volumes of air flow, this result beingaccomplished by restricting the air bleed orifice as indicated at 90 inFigure 12.

It will thus be seen that I have invented an improved and simplifiedcarburetor having greatly improved metering characteristics over anincreased operating range giving higher specific power outputs for agiven engine without adversely affecting the economical operationthereof at part loads.

I am aware that many changes may be made and numerous details ofconstruction may be varied through a Wide range without departing fromthe principles of this invention, and I therefore do not purposelimiting the patent granted hereon otherwise than necessitated by theprior art.

I claim as my invention:

1. A carburetor having in combination a body containing an air intakepassage leading to a venturi and a mixture outlet passage therefrom,

. a throttle valve controlling the flow through said passages, a primarysuction responsive fuel supply including a nozzle discharging at thethroat of said venturi, a'secondary fuel supply also discharging at thethroat of said venturi, said secondary fuel supply including means formaintaining a positive static head relative to the point of discharge,and means responsive to suction in the carburetor passages on the engineside of the throttle valve for cutting off said secondary fuel supply inresponse to high suctions in said passages.

2. A carburetor having in combination a body containing an air intakepassage leading to a venturi and a mixture outlet passage therefrom, athrottle valve controlling the flow through said passages, a primarysuction responsive fuel supply including a nozzle discharging at thethroat of said venturi, a secondary fuel supply also discharging at thethroat of said venturi, said secondary fuel supply including means formaintaining a positive static head relative to the point of discharge,and means adapted to shut off said secondary fuel supply under idlingconditions.

3. A carburetor of the class described comprising a body member having asuitable air passage therethrough, including a venturi and throttlevalve in said passage, primary and secondary fuel metering systemshaving separate metering and delivery orifices, a well supplying fuelunder a gravity head to said secondary fuel metering system, valve meansfor controlling the fuel delivery from said well, a float chambersupplying fuel to the primary fuel metering system in response tosuction thereon, means for supplying excess fuel to said well and forconducting the excess fuel from said well to the float chamber, and afloat actuated valve controlling the admission of fuel to the well.

4. A carburetor of the class described comprising a body member having asuitable air passage therethrough, including a venturi and throttlevalve in said passage, primary and secondary fuel metering systemshaving separate metering and delivery orifices, a well supplying fuelunder a gravity head to said secondary fuel metering system, meansadapted to shut off the secondary fuel metering system under idlingconditions, a float chamber supplying fuel to the primary fuel meteringsystem in response to suction thereon, means for supplying excess fuelto said well and for conducting the excess fuel from said well to thefloat chamber, and a float actuated valve controlling the admission offuel to the well.

5. A carburetor comprising a well, a fuel supply therefor, a constantlevel fuel reservoir at a lower level relative to the well, an overflowpassage from said well to the reservoir, a nozzle connected to the welland located below the fuel level therein whereby a positive static fuelhead is maintained on the fuel delivered from said nozzle, and means forair bleeding the fuel supply to said nozzle to reduce the effect ofsuction thereon.

6. A carburetor comprising a well, a fuel supply therefor, a constantlevel fuel reservoir at a lower level relative to the well, an overflowpassage from said well to the reservoir, a nozzle connected to the welland located below the fuel level therein whereby a positive static fuelhead is maintained on the fuel delivered from said nozzle, means for airbleeding the fuel supply to said nozzle to reduce the effect' of suctionthereon, and means for cutting off the flow of fuel to said nozzle underidling conditions.

'7. A carburetor comprising a well, a fuel supply therefor, a constantlevel fuel reservoir at a lower level relative to the well, an overflowpassage from said well to the reservoir, a nozzle connected to the welland located below the fuel level therein whereby a positive static fuelhead is maintained on the fuel delivered from said nozzle, means for airbleeding the fuel supply to said nozzle to reduce the effect of suctionthereon, and suction responsive means adapted to cut off the flow offuel to said nozzle at high engine suctions.

8. A carburetor comprising a well, a fuel supply therefor, a constantlevel fuel reservoir at a lower level relative to the well, an overflowpassage from said well to the reservoir, a nozzle connected to the welland located below the fuel level therein whereby a positive static fuelhead is maintained on the fuel delivered from said nozzle, means for airbleeding the fuel supply to said nozzle to reduce the effect of suctionthereon, and a second nozzle connected to the fuel reservoir and adaptedto draw fuel therefrom in response to suction on said nozzle.

9. A carburetor comprising a well, a fuel supply therefor, a constantlevel fuel reservoir at a lower level relative to the well, an overflowpassage from said well to the reservoir, a nozzle connected to the welland located below the fuel level therein whereby a positive static fuelhead is maintained on the fuel delivered from said nozzle, valve meansfor controlling the fuel delivery from said well, and a second nozzleconnected to the fuel reservoir and adapted to draw fuel therefrom inresponse to suction on said nozzle.

10. In a carburetor having a primary fuel supply system including afloat chamber and fuel delivery means, a secondary fuel supply systemsupplementing the primary fuel supply system, comprising a fuel nozzle,means for supplying fuel to said nozzle under a gravity head, andsuction responsive means for coordinating the supply of fuel from saidnozzle with that of the primary fuel supply system whereby to provide abalanced fuel and air mixture in the carburetor over the operating rangethereof.

11. In a carburetor having a primary fuel supply system including afloat chamber and fuel delivery means, a secondary fuel supply systemsupplementing the primary fuel supply system, comprising a fuel nozzle,means for supplying fuel to said nozzle under a gravity head, andsuction actuated means adapted to cut off the secondary fuel supply at apredetermined high suction whereby the secondary fuel supply systemsupplements the primary fuel supply system at operating conditions abovesmall loads.

CHARLES H. KIRBY.

